Decoherence and Decay of Two-level Systems due to Non-equilibrium Quasiparticles

TL;DR

This paper investigates how non-equilibrium quasiparticles in superconductors cause decay and decoherence in two-level systems, affecting quantum device performance at low temperatures.

Contribution

It provides a detailed analysis of decay laws for TLS interacting with quasiparticles, considering various experimental conditions and distributions.

Findings

Quasiparticles induce TLS decay even at very low temperatures.

Decay laws depend on quasiparticle distribution and interaction form.

Results inform strategies to mitigate decoherence in superconducting qubits.

Abstract

It is frequently observed that even at very low temperatures the number of quasiparticles in superconducting materials is higher than predicted by standard BCS-theory. These quasiparticles can interact with two-level systems, such as superconducting qubits or two-level systems (TLS) in the amorphous oxide layer of a Josephson junction. This interaction leads to decay and decoherence of the TLS, with specific results, such as the time dependence, depending on the distribution of quasiparticles and the form of the interaction. We study the resulting decay laws for different experimentally relevant protocols.